It’s a great story, perfectly suited for a theater or movie adaptation: the final moments of the Ptolemaic queen Cleopatra, who had herself bitten by a viper. There is indeed ancient evidence for this story, which is told by Plutarch (Marc Antony, 86):
It is said that the viper (aspis) was brought with those figs and leaves and lay hidden beneath them, for thus Cleopatra had given orders, that the reptile might fasten itself upon her body without her being aware of it. But when she took away some of the figs and saw it, she said: “There it is, you see,” and baring her arm she held it out for the bite.
However, this cannot be true. A viper’s bite is not fatal. Only a few scholars have realized the problem, and they have argued that in fact a cobra must be meant. However, the Greeks and Romans were perfectly capable of distinguishing several kinds of snakes. The poet Lucian even offers a catalog of reptiles (with their poisonous effects) in his Pharsalia, book nine.
I do not know what really happened, but I have an idea: Octavian sent a soldier to kill the queen, because he could not afford to capture her. Just imagine that he returned to Rome with a woman tied to his triumphal chariot. The Romans would joke that he had not won a major war, but had merely defeated a woman. There is, of course, no evidence for this theory, but at least it is possible. That’s more than we can say about a fatal viper’s bite.